From: Martin Schwidefsky <schwidefsky@de.ibm.com>

I think I found a potential race in install_page/install_file_pte. The
inline function zap_pte releases pages by calling page_remove_rmap and
page_cache_release.  If this was the last user of a page it can get
purged from the page cache and then get immediatly reused. But there
might still be a tlb for this page on another cpu. The tlb is removed
in the callers of zap_pte, install_page and install_file_pte, but this
is too late. I admit that its a very unlikely race but never the less..

I fixed this by using the new ptep_clear_flush function that is introduced
with the tlb flush optimization patch for s/390.